That PCB screams Radio Shack. That's what I was thinking before you showed us the RS catalog. They used the same double sided boards with printed resistors in their scanners. These PCB boards were problematic because the through hole vias would break the connection. The fix was to insert a piece of wire through the hole and solder both sides to re-establish a connection Great job on the pot fix, thanks for sharing your expertise
Yea, when I seen the onboard resistors I could just sense something to do with that might be the issue, I rarely need a schematic for anything but having one for this would have solved the mystery.
